Trace Evidence: Hair - Dr. Hall's Science Site · 2019. 8. 16. · Significance of Hair Evidence...
Transcript of Trace Evidence: Hair - Dr. Hall's Science Site · 2019. 8. 16. · Significance of Hair Evidence...
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Trace Evidence: HairForensic Science
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Hair is…• A slender threadlike outgrowth from the
follicles of the skin of mammals
• Found all over our bodies
– Head
– Face
– Chest
– Limbs (arms and legs)
– Pubic region
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Because many people have similar hair structure and color, hair is considered class evidence.
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Structure
• Major components
– Keratin is a protein that makes up most of the hair shaft.
– Melanin is a pigment that gives hair its color.
– Redheads have pheomelanin instead of melanin.
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Structure – pencil analogy
• Cortex – the main body (wooden portion)
• Medulla – the central cell of the cortex that is not always present in every hair (pencil lead)
• Cuticle – a layer of scales covering the hair shaft (yellow paint)
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Hair
vs.
Pencil
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Structure (continued)
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Characteristics
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Medulla Variations
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ContinuousClear Medulla
Continuous Opaque Medulla
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Medulla Variations
Wafer MedullaDiscontinuous Medulla
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Medulla Variations
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Bubbly or Cellular Medulla
Coarse CellularAppearance
(no visible medulla)
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Pigment
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• Colors – light, medium, dark; reddish-brown,
brown, black, etc.
• Granual Sizes – fine, moderate, large
• Density – light, moderate, heavy
• Distribution – random, peripheral, even,
central, one-sided
Dyed Human
Hair
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Pigment Distribution
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One-SidedPeripheral in Human Hair
Central in Red Human Hair
Random in Animal Hair
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Ovoid Bodies
• Ovoid bodies – spherical to oval heavily pigmented structures found mostly in cattle and dog hairs, but present in some human hairs
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Ovoid Bodiesin human hair
Ovoid Bodiesin dog hair
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Cortical Fusi
• Cortical fusi – elongated, spindle-shaped air spaces in the cortex
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Root (Proximal End): Growth Stages• Anagen root – an active growth stage, often found with a
ribbon-like tip and a follicular tag (a soft tissue from the follicle)
• Catagen root – the intermediate stage of growth
• Telogen root – a resting stage, has a bulb-like shape. Often
found with very little pigment and an abundance of cortical fusi.
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Roots (continued)
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Anagen Catagen
Telogen
follicular tag
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Follicular Tag
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• Hairs that are forcibly removed often end up with a follicular tag (a soft tissue from the follicle) attached to the roots.
• The follicular material may be suitable for nuclear DNA analysis.
telogen root without follicular tag
telogen root with follicular tag
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Roots (continued)• Postmortem Root Band (aka "Dead
man's root”) a dark band that may appear near the root of the hair originating from a decomposing body
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Other Distal End Configurations
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Scissor-cut Abraded
Rounded
Broken
Razor-cut
Burnt hair
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Hair – Racial Origin• Hair from people of different ethnic origin has distinctive
characteristics that can be compared in the forensics lab
• Anthropologists classify humans into groups based on phenotypic characteristics such as cranial and skeletal morphology
– Caucasoid: descendant of peoples indigenous to Europe, N Africa, SW Asia, and the Indian subcontinent
– Mongoloid: descendant of peoples indigenous to central and eastern Asia; also Eskimos and Native Americans
– Negroid: descendant of peoples indigenous to sub-Saharan Africa
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Racial Origin
• Hair characteristics that can be compared in the forensics lab include:
– shaft diameter
– shape of cross-section
– pigment density and distribution
– cuticle thickness, etc.
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Racial Origin
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• Caucasoid
– moderate shaft diameter with very little variation
– light to moderate pigment density with fairly even distribution
– oval-shaped cross-section
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Racial Origin (continued)
• Mongoloid
– coarse shaft diameter
– streaky pigments with heavy density
– thick cuticle
– round cross-section
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Racial Origin (continued)
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Mongoloid Head Hairs
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Racial Origin (continued)
• Negroid– fine to moderate shaft
diameter
– considerable variation throughout the hair shaft with prominent twists and curls
– heavy pigment density with pigment clumpings
– flattened cross-section
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Racial Origin (continued)
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Negroid head hairs
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VariationsWhy do we need to examine each hair sample from root to tip?
Five Regions of a single head hair
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Variations (continued)
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One person'shead hair
One person of multiple race
These within-individual variations are why it’s important to sample multiple hairs from each suspect.
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Somatic (Body Area) OriginHairs from different parts of the body exhibit
different characteristics:
• Head hairs
– Typically much longer than other hairs on the body
– Generally soft and most likely to have artificial
treatment (bleaching, dyes)
• Pubic hairs
– Typically coarse in diameter with wide
variations
– Buckling/bending is a special
characteristic found in pubic hairs
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Somatic Origin (continued)• Limb hairs (arm or leg)
– Fine diameter with little variation
– Arc-like, gross appearance
– Tips are usually tapered, often blunt and
abraded, rounded scale ends due to wear
– Soft texture
• Facial hairs (beard/mustache)
– Very coarse diameter with irregular or
triangular cross-sections
– Very broad and continuous medulla
– Medulla may be double
– Stiff texture30
Beard hair
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Somatic Origin (continued)• Chest hairs
– Moderate and variable shaft diameter; tips often
darker in color
– Long and fine, arc-like
– May have granular medulla
– Stiff
• Auxiliary (underarm) hairs
– Resemble pubic hairs in general appearance, but less
buckling
– Fine tip
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• Other body hairs
– Eyebrow: stubby, saber-like
appearance
– Eyelash: short and stubby,
with a saber-like appearance
– Trunk: a combination of limb
and pubic hairs
Somatic Origin (continued)
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Human vs. Animal Hair
3 Main Differences:
• pigment/color pattern
• medulla thickness and shape
• cuticle scale shape
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Human hair color is fairly
constant throughout the
shaft whereas animal
hair can abruptly change
color.
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Human vs. Animal Hair - Medulla
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The medulla is typically wider and more well defined in animal hair.
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Human Animal
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Human vs. Animal Hair - Medulla
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Rabbit hair
Uniserial Ladder Medulla
Multiserial Ladder Medulla
Rabbit hair
The medulla in animal hairs can have a very distinctive pattern.
Cellular Medulla
Opossum hair
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Human vs. Animal Hair - Scales
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Imbricate Scales Diagram (humans have this)
Coronal Scales Diagram Spinous Scales Diagram
The cuticle (outer layer) of hair is made up of overlapping scales that have different shapes in different organisms.
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Human vs. Animal Hair - Scales
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coronal scales in bat hairimbricate scales in human hair
spinous scales in mink hair
isodiametric scalesin deer hair (like fish scales)
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Human vs. Animal Hair
3 Main differences
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Human Hair Animal Hair
Pigmentcolor and pigmentation is
constant throughout the hair shaft
can have abrupt color changes
Medullathin, ~1/3 of the hair shaft diameter; amorphous
very wide, well-defined (with certain patterns)
Scale Structure
has overlapping imbricate scales
varies widely; may be imbricate, coronal, spinous,
etc.
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Animal Hairs Identification
• 2 types of animal hairs
– Guard hair: coarse diameter, provides protection, “outer fur”
– Fur hair: fine diameter, provides insulation, “under fur”
• 3 major groups identified by microscopic appearance
– Deer and antelope family
– Commercial fur animals (rabbit, mink, etc.)
– Domestic animals
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Deer and Antelope Family
• Distinguished based on their isodiametricscales (like fish scales) and wineglass-shaped root
• Deer
• Caribou
• Elk
• Moose
• Antelopes
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Commercial Fur Animals
• Rabbit
• Mink
• Muskrat
• Chinchilla
• Seal
• Raccoon
• Fox
• Beaver
• Bear
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rabbit
muskrat seal
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Domestic Animals
• Generally amorphous medullae• Characteristic root shapes• Dog• Cat• Cattle• Horse
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cat
dog
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Domestic Animals (continued)
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cat hair root dog hair root
• Elongated• No distinct shape• Fibrils frayed at base of root
• Spade-shaped root
It is usually necessary that the root be present in order for one to distinguish between dog and cat (or between cattle and horse).
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Domestic Animals (continued)
• Cattle hair
– Very coarse diameter
– Abundance of ovoid bodies
– Medullae continue into the elongated root area
• Horse hair
– Few ovoid bodies
– Bulb-shaped root
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Diseases affecting hair• Certain diseases or deficiencies may result in changes in
the appearance of hair.
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Pili annulati –ringed or banded hairs
Trichorrhexis nodosa -conspicuous nodes due to immunodeficiency or small bowel disorder
Parasites - egg sack of head lice
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Hair Comparisons
• Comparison microscope
– 2 compound microscopes connected together with an optical bridge
– Enables side-by-side comparisons
– Typical magnification from 100X to 250X
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Hair Comparisons (continued)• Information NOT provided by a hair examination
– Age– Gender– Unless nuclear DNA analysis is performed on its
follicular tag
• Information provided by a hair examination– Is it human or animal hair?– What is the possible race of the donor?– What area of the body did it come from?– Could it have originated from the donor of the known
standards?
• Hair can also be used to distinguish between identical twins (who cannot be distinguished based on their DNA).– because of the environmental effects on hair such as
• weather exposure, diet, artificial treatment, etc. 47
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Three conclusions that can be reached in hair comparisons:
1) Similar microscopic characteristics – the questioned hairs could have originated from the source of the known hair standards. (Hair is class evidence!)
2) Dissimilar microscopic characteristics – the questioned hairs did not originate from the source represented by the known hair standards
3) Both similar and slightly different microscopic characteristics – inconclusive
Hair Comparisons (continued)
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Significance of Hair Evidence
• The frequency of contact between a victim and a suspect, as well as the crime scene, is a big factor in interpreting the significance of hair evidence.
• Examples
The pubic hair of a recent ex-boyfriend found at the scene of a sexual assault
A husband who is suspected of murdering his wife at home
A missing child's hair in the backseat of a former nanny's car
A missing child's hair in the backseat of a cleaning lady's car
A stepfather's head hair found on a little girl's underwear
A stepfather's pubic hair found in the crotch area of a little girl's underwear
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Resources
• Saferstein, Richard. Forensic Science: An Introduction. New Jersey: Pearson Prentice Hall, 2008.
• Saferstein, Richard. Criminalistics: An Introduction to Forensic Science. 8th ed. Upper Saddle River, NJ: Pearson Prentice Hall, 2004.
• Saferstein, Richard. Forensic Science Handbook. Englewood Cliffs, NJ: Prentice-Hall, 1982.
• Bertino, Anthony J. Forensic Science: Fundamentals and Investigations. Mason, OH: South-Western Cengage Learning, 2009.
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